It is, as is well known, frequently necessary to measure the hardness of a film (for instance of a finger nail varnish film or the film of paint, varnishes, plastic materials, coatings and the like and so forth); and, more generally, of all materials capable of forming skins. To do this, a standardised measure has been developed and defined. This generally uses a pendulum whose oscillating arm rests on the film to be tested. The damping time of the pendulum oscillation is measured, during which time it passes from an angular amplitude .alpha. to a lower angular amplitude .beta.. Provision is made for the pendulum to rest on the film to be tested by means of two half spheres and for the structure of the oscillating pendulum mass to be arranged so that the pendulum should impact on the second one.
In a first embodiment of such a device, widely known in the art and called a "PERSOZ" pendulum, an angle of 12.degree. has been adopted for .alpha. and of 4.degree. for .beta.. In another and second embodiment, generally referred to as "KONIG'S pendulum", a value of 6.degree. has been adopted for .alpha. and 3.degree. for .beta..
In embodiments of the known and mentioned type, a disc of standardised dimensions is positioned on the apparatus carrying the film to be tested. Then the two hemispheres of the pendulum are manually brought to bear on the film. Finally, the pendulum arm is taken to one extreme of its initial oscillating course of and for the value .alpha.. After that, the pendulum is released; and the time necessary for the pendulum arm to come to oscillate up to an amplitude of value .beta. is measured.
It is apparent that there exist many sources of possible errors in the course of the various above-explained measurement stages and steps. In illustration of this, it must be reckoned that:
In the first place, the positioning of the pendulum on the specimen must be effected without any deterioration in the zone of the film to be measured.
Also and secondly, it is necessary to bring the pendulum arm into a position exactly corresponding to angular amplitude .alpha.. In other words, it is necessary for this procedure to effect a setting in a plane strictly perpenducular to the line joining the two bearing points of the pendulum on the film.
Thirdly, the apparatus must be adjusted so that the plate supporting the film should be strictly horizontal to avoid any slide of the pendulum on the film during the course of the measurement.
Fourthly, from the moment when the pendulum arm is released, it is necessary for the operator to count the time and to turn off or stop the stop-watch (or other time-measuring device) exactly at the moment when the oscillation amplitude becomes equal to the predetermined angle .beta.. This latter synchronisation is, for all practical purposes, rather difficult to achieve. It also entails a relatively wide scatter of the results obtained for the same measurement. Moreover, the operator is obliged to be permanently present during the whole time of the measurement. And, should the operator have to move the supporting plate for the film in order to do another measurement, it is necessary to effect the handling and then again be present during the whole duration of the subsequent measurement.